rotateBy: angle about: center 

    "Even though Point.theta is measured CW, this rotates with the more conventional CCW interpretateion of angle."

[...]

I think this comment does not explain what this method does.

What should be something like:

This method returns the point obtained after rotating myself around #center point of an #angle given as parameter. The #angle provided as parameter is interpreted as being in radian.

Additionally, I think the name of this method is bad, maybe it should be renamed to something more explicit like #rotateBy:around: or #rotateByRadians:around:.

Maybe, if this method is renamed as #rotateByRadians:around:, the method #rotateByDegrees:around: should be added as well.

Cheers,

Julien